Process for preparing coal veins for gasification by removal of underlying clay



July 1951 F. SQUIRES 2,561,639

PROCESS FOR PREPARING COAL VEIINS FOR GASIFICATION BY REMOVAL OF UNDERLYING CLAY Filed June 29, 1949 3 Sheets$heet l s my Emma 'nl-u u-plurepn IN V EN TOR.

A T TORIVEYS July 24, 1951 F. SQUIRES 2,561,639

PROCESS FOR PREPARING COAL VEINS FOR GASIFICATION BY REMOVAL OF UNDERLYING CLAY I5 Sheets-Sheet 2 Filed June 29, 1949 T r t ja JMJ WW A TTORNEYS July 24, 1951 F. SQUIRES 2,561,639

PROCESS FOR PREPARING COAL VEINS FOR GASIFICATION BY REMOVAL OF UNDERLYING CLAY Filed June 29, 1949 3 Sheets-Sheet 3 5' U CCES 5/ V5 CLA Y REMO VAL IN V EN TOR,

A T TOR/VEYS Patented July 24, 1 951 UNITED STATES PATENT OFFICE" PROCESS FOR PREPARING COAL VEIN S FOR GASIFICATION BY REMOVAL OF UNDER- LYING CLAY Frederick Squires, Champaign, Ill. Application June 29, 1949, Serial N0. 101,997

4 Claims. 1

The present invention relates to a process for preparing coal veins for gasification in situ in the earth by removal of the clay underlying the coal veins to expose the undersurfaces of the coal veins. Gasification of coal in situ in the earth requires an inlet for air or other combustion supporting gas, a fire in the coal and an outlet for the gaseous products. It has heretofore been proposed to dig an inlet shaft from the surface of the earth to the coal vein. to form a tunnel through the coal vein, and to dig a second shaft from the surface of the earth to the end of the tunnel opposite the inlet shaft, this second shaft forming an outlet for the gaseous products. In the practice of this prior proposal the coal is burned along the sides of the tunnel. Combustion of the coal results in formation of ash which soon smothers combustion and tends to choke the tunnel. Insufiicient coal is exposed for combustion to justify the expense of forming the inlet and outlet shafts and the tunnel through the coal vein.

My invention relates to a procedure or process which overcomes the difficulties outlined above and which greatly reduces the cost of preparing coal veins for gasification. My process involves the drillingof two or more horizontally spaced wells from the surface of the earth through the coal vein and into the clay underlying the vein. The clay immediately underlying most coal veins is readily water dispersible and by discharging water laterally from the wells into this clay I am able to form large cavities or voids surrounding the wells and immediately underlying the coal vein. Water under high pressure can then be introduced into the bottom of one or more of the 'wells and this pressure forces breaks in the remaining clay between the wells which has not already been removed. I then flow water between the wells through the breaks and additional clay is dispersed to enlarge the breaks and to form passageways between the wells. The roof of the voids surrounding the wells and of the communicating passageways between wells is formed by the lower surface of the coal vein. This surface of the coal vein can be exposed for combustion by removing the water from the wells and from the voids and passageways in the underlying clay. The lower surface of the coal vein can then be ignited and combustion will proceed from the bottom of the vein upwardly therethrough. Ash formed by combustion will not close the voids and passageways for the reason that depletion of the coal by combustion increases the height or thickness of the voids and passageways. Large areas of the undersurface of the coal vein are exposed by my process and combustion over these substantial areas proceeds readily because of the fact that the combustion occurs at the lower surface of the coal.

Among the objects of my invention are to provide a simple and inexpensive procedure for preparing coal veins for gasification in situ in the earth, to provide a procedure which can be practiced with readily available equipment which ls inexpensive. to provide a process which exposes large areas of the undersurface of the coal veins for efllcient combustion and to provide a process which recovers large quantities of clay which is suitable for manufacture of fire bricks in a location where combustible gases are available for burning the bricks.

The foregoing and other objects and advantages of the invention will be more fully understood from the following detailed description which has reference to the accompanying drawings wherein:

Fig. 1 is a vertical sectional view showing the manner in which voids are formed in the water dispersible clay underlying the coal vein and illustrating suitable apparatus for forming these voids;

Fig. 2 is a vertical sectional view comparable to Fig. 1 showing the manner in which the voids are simultaneously produced beneath the coal vein around two horizontally spaced wells;

Fig. 3 is a horizontal sectional view taken in the direction of the arrows along the line 3-3 of Fig. 2;

Fig. 4 is a vertical sectional view illustrating the manner in which a break is forced through the clay underlying a coal vein between horizontally spaced wells and also illustrating the manner in which the break is enlarged to form a passageway between these wells;

Fig. 5 is a horizontal sectional view taken in the direction of the arrows along the line 5--5 of Fig. 4;

Fig. 6 is a horizontal sectional view through the clay underlying a coal vein and illustrates three horizontally spaced wells which have been placed in communication with each other by my process;

Fig. 7 is a vertical sectional view illustrating one procedure which is suitable for removing the water from the voids and passageways beneath the coal vein to expose the lower surface of the coal vein for combustion;

Fig. 8 is a horizontal sectional view taken in the direction of the arrows along the line 8-8 of Fig- 7;

ataaese typical sequence of coal veins in a coal basin;

and

Fig. 12 is a horizontal sectional view illustrating a suitable arrangement of input and output wells communicating with a void underlying a coal vein.

The reference numeral I3 designates a subterranean coal vein covered by the earth formation ll. Such a coal vein usually overlies an underclay I5 of readily water dispersible clay which is suitable for the manufacture of fire bricks. Beneath the underclay Hi there is usually a stratum of calcareous clay it which is not water dispersible to any appreciable extent. A stratum of limestone l1 conventionally underlies the calcareous clay i6.

A well bore 18 is drilledthrough the earth formation i4 and the coal vein l3 into the stratum of water dispersible clay IS. The well bore is preferably provided with a casing I9 which may be surrounded by a layer 20 of fire-proof cement. A pump 2|, which may be of the type known in the drilling art as a mud pump, pumps water from near the upper surface of a settling tank 22 through an inlet pipe 23, an outlet pipe 24 and a. tubing 25 which extends through the casing IE! to the bottom of the well. The lower end of the tubing 25 is provided with any suitable nozzle means for directing jets of water horizontally against the stratum of water dispersible clay 15. The nozzle means is designated by the reference numeral 26 and preferably includes some suitable means for rotation to cause the horizontal jets to impinge on the clay strata l5 in all horizontal directions from the well.

Jets of water from the nozzle means l6 strike the stratum 15 of water dispersible clay and the clay becomes dispersed in the water. Any suitable agents may be added to the water to increase the amount of clay becoming dispersed through the mechanical action of contact of the jets of water. Gas may be entrained in the water to increase agitation at the bottom of the well if this seems desirable. Water with clay dispersed therein flows upwardly in the annular Figs. 2 and 3 illustrate the well i8 and a slmi lar well 28 laterally spaced therefrom. The well 28 is preferably also provided .with the equipment described above. The water jets form a void 29 in the water dispersible clay l5 at the bottom of the well i8 and a similar void 30 at the bottom of the well 28. As the voids 29 and 30 become larger, the distance between the adjacent edges of the voids becomes less, as will be apparent from Fig. 3. This distance will eventually become sufficiently small that it .is possible to force a break through the clay stratum 15 by increasin the pressure at the bottom of one or both wells. The pressure at the bottom of the wells can be increased by closing the valves 3| in the outlet conduits 21 while the pumps 2| the form of a generally horizontal fissure Figs. 4 and 5 illustrate the manner in whichthe break can be enlarged to expose additional portions of the undersurface of the coal vein IS. The pump 2! associated with the well l8 is'permitted to continue operation, while the corresponding pump 2'! associated with the well 23 is not functioning. Clay which forms the walls of the break becomes dispersed in the water flowing through the break and the break gradually enlarges to form the passageway 32. A large volume of clay is thus removed from beneath the coal vein. I

In some instances the voids 29 and 30 may be enlarged by the jets of water from the wells to an extent sufllcient to cause them to overlap or communicate with each other. In the instances the use of water pressure to force a break through the clay will be unnecessary.

Fig. 6 illustrates my process as applied to three horizontally spaced wells which are designated by the reference numerals 33, 34 and 35. Generally circular voids are first formed in the water dispersible clay surroundin each of these wells in the manner described above. The pressure in one or more of the wells may then be increased to form the initial breaks through the ences in the degree of shading in Fig. 6 illustrate various stages in the ,progress of removal of the water dispersible clay from beneath the coal vein The.unshaded area 36 has already had the clay removed therefrom and the area from which the clay becomes removed will gradually increase in size as the circulation of water around and between the wells continues.

Figs. 7 and 8 illustrate one suitable method for driving the water from the voids at the bottom of a .pair of wells and from the passage connecting those voids. Compressed air is introduced into the well l8 through a conduit 31. This compressed air will drive the water 38 from the voids and passageways and outwardly through the well 23. Removal of the water exposes the undersurface of the coal vein.

Figs. 9 and 10 illustrate the manner in which combustion proceeds on the exposed lower face of the coal vein. Combustion is started in any suitable manner on the lower surface of the coal vein adjacent the well i8. Air or other combustion supporting gas is introduced into the well ill through the conduit 31. The products of combustion pass upwardly through the well 28 and are conveyed through the conduit 39 to suitable collectin and recovering apparatus not shown.

The nature or character of the products of combustion can be controlled by controlling the amount of combustion supporting gas supplied through the well I8. The earth formation provides excellent heat insulation and considerable heat can be applied to the coal vein with a minimum of actual active combustion of the coal. The temperature of the coal vein can be controlled' by controlling the fire and many valuable products can be derived from the coal and recovered in the gaseous products which are continue to operate. The break will usually take 76 wells prevents excessive loss of heat from the is used for gasification 11 illustrates a geologic column which includes a ing my invention.

hot gaseous products and thus prevents trouble from condensation.

The clay which is recovered by my process is suitable for manufacture of fire bricks. The gasification of the coal prdouces inflammable gases which are available for firing the bricks. The clay and the fuel for burning the bricks are thus available at. the same site.

I have heretofore described my process as it of a single coal vein. Fig.

plurality of coalveins coal vein are shown water dispersible clay, calcareous clay and limestone. My process as described above may be used to expose the lower surface of the uppermost coal vein and the process may then be repeated on successively lower coal veins. Alternatively, the process of the invention can be used to expose the lower surface of plurality of coal veins simultaneously. Gasiflcation of the coal veins may then proceed successively or concurrently. Heat evolved duringgasiflcation of one coal vein will aid in the concurrent or subsequent gasification of other coal veins in the formation. It is advantageous to remove the clay from beneath the uppermost coal vein first for the reason that the void thus produced reduces the overburden over lower veins and facilitates forming the breaks through the clay underlying lower coal veins.

Fig. 12 illustrates a suitable arrangement of input and output wells for gasification of a coal vein overlying the clay strata l5. After combustion has been started air or other combustion supporting ga is introduced through the input wells 40, 4| and 42, and the gaseous products are vented through the output wells 43, 44, 45 and 46. Other arrangements of input and output wells may be used and that illustrated in Fig. 12 is given by way of example only.

The layer of water dispersible clay underlying a coal vein is usually thin and since it overlies a layer of calcareous clay which is not readily dispersible by water, the amount of material which must be removed to expose the undersurface of the coal vein is relatively small. It sometimes happens that the strata of calcareous clay is missin and in those instances the water dispersible clay immediately overlies the limestone. The limestone is not appreciably dispersed by water so in these instances the water dispersible clay strata is all the material that need be removed to expose the undersurface 01' the coal vein.

I have illustrated and described what I now consider to be the preferred process for practic- It is to be understood, however, that various alterations and modifications may beresorted to without departing from the broader scope of my invention as defined by the following claims.

Having thus described my invention, I claim:

1. A process for preparing coal for gasiflcation in situ in the earth which comprises drilling a at different levels. These as separated by layers of creasing the pressure in at pair of horizontally spaced wells through an underground coal vein into the clay stratum underlying said coal vein, discharging water laterally from each well into said clay stratum to disperse the clay surrounding the well, flowing the water dispersed clay upwardly through the wells, increasing the pressure of the water in at least one of said wells to force a break in the remaining clay between said wells, flowing water from one well to the other through such break to form an enlarged passageway between said wells, and displacing the water in said wells and said passageway by air to support combustion along the undersurface of the coal vein.

2. A process for preparing coal for gasification in situ in the earth which comprises drilling a plurality of spaced wells through an underground coal vein into the water dispersible clay stratum underlying said coal vein, discharging water laterally from each well into said clay stratum to disperse the clay and to form a void around each .well beneath the coal vein, flowing the water dispersed clay upwardly through the wells, increasing the pressure in at least some of said voids to force breaks in the clay remaining between said voids, flowing water between wells through such breaks to disperse additional clay and to form enlarged passageways between said voids, and displacing with air the water in said voids and passageways to support combustion along the undersurface of the coal vein.

3. A process for preparing a plurality of vertically spaced coal veins for gasification in situ in the earth which comprises drilling a plurality of spaced wells through said coal veins and through the water dispersible clay strata underlying said coal veins, discharging water laterally from each well into said clay strata to disperse the clay and to form voids around each well beneath each coal vein, flowing the water dispersed clay upwardly through the wells, in-

least some of said wells to force breaks through the clay remaining between the voids, flowing water through such breaks to disperse additional clay and to form enlarged passageways connecting the voids, and displacing the water in said voids and passageways with air to facilitate combustion along theundersurfaces of the coal veins.

4. A process for preparing coal for gasiflcation in situ in the earth which'comprises drilling a pair of spaced wells through the coal vein into the water dispersible clay stratum underlying said coal vein, discharging water laterally from each well into said clay stratum to disperse the clay and to form voids surrounding each well beneath said coal vein, flowing the water dispersed clay upwardly through the wells, continuing to disperse the clay until said voids are in communication with each other, and then displacing the water in said voids with air to facilitate combustion along the undersurface of the coal vein.

FREDERICK SQUIRES.

No References Cited. 

